A154525
Primes p such that lcm(1,2,3,...,p-2,p-1,p) + 1 is prime.
Original entry on oeis.org
2, 3, 5, 7, 19, 31, 47, 89, 127, 139, 2251, 3271, 4253, 4373, 4549, 5449, 13331, 37123, 55291
Offset: 1
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Select[Range[1000], PrimeQ[#] && PrimeQ[LCM@@Range[#]+1] &] (* Amiram Eldar, Nov 21 2018 *)
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isok(p) = isprime(p) && (isprime(lcm(vector(p, i, i)) + 1)); \\ Michel Marcus, Oct 26 2013, Feb 25 2014
a(1)=2 inserted and a(8)-a(18) from
Ray Chandler, Jan 16 2009
A154526
Primes p such that lcm(1,2,3,...,p-2,p-1,p) -+ 1 are both primes.
Original entry on oeis.org
3, 5, 7, 19, 47
Offset: 1
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isok(p) = {if (! isprime(p), return (0)); lcmv = lcm(vector(p, i, i)); isprime(lcmv + 1) && isprime(lcmv - 1);} \\ Michel Marcus, Oct 26 2013
A385564
Prime powers k such that lcm(1, 2, 3, ..., k)-1 is prime.
Original entry on oeis.org
3, 4, 5, 7, 8, 19, 23, 29, 32, 47, 61, 97, 181, 233, 307, 401, 887, 1021, 1087, 1361, 1481, 2053, 2293, 5407, 5857, 11059, 14281, 27277, 27803, 36497, 44987, 53017
Offset: 1
k=32 is a prime power, so point at which A003418 attains a new value, namely lcm(1, 2, 3, ..., 32) = 144403552893600, and by subtracting one we get 144403552893599 which is a prime number, so 32 is a member of the sequence.
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Select[Range[6000],PrimePowerQ[#]&&PrimeQ[Fold[LCM,Range[#]]-1]&] (* James C. McMahon, Jul 09 2025 *)
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L=1;for(k=2,6000,!isprimepower(k,&p)&&next();L*=p;ispseudoprime(L-1)&&print1(k,", "))
Showing 1-3 of 3 results.
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